EVLN(Iron and nitrogen batteries last longer)
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--- {EVangel}
http://www.nature.com/nsu/010913/010913-5.html
Rechargeable batteries get boost
New material could mean more mobile talk and type time.
10 September 2001 PHILIP BALL
Iron and nitrogen batteries last longer. � Corbis
A new material might help rechargeable batteries last longer
before needing a boost from the mains - good news for the
rapidly expanding portable electronics industry.
By 2003 the market for rechargeable lithium batteries could
be worth over $2 billion in the United States alone, owing
to their use in devices such as laptops and cell phones.
Most rechargeable batteries are made of lithium, with cobalt
compounds in one of the electrodes. Cobalt would improve the
other electrode too, giving a longer battery life, but it is
expensive and mildly poisonous.
Linda Nazar and colleagues at the University of Waterloo in
Canada have come up with an iron and nitrogen alternative1.
Preliminary tests show that the lithium iron nitride
compound stands up well to repeated charging and
discharging. The material's 'capacity' is also comparable to
other leading candidate compounds. Capacity is the amount of
current a substance provides, and for how long, per gram. A
powerful battery is no good if it is too heavy.
A rechargeable lithium battery has two terminals: the
negative electrode, or anode, and the positive electrode, or
cathode. The anode in most commercial cells is graphite or
some other carbon-based material. The cathode is usually
made of lithium cobalt oxide.
Both electrode materials have a layered structure which
lithium ions can be inserted into and removed from. The
movement of lithium ions from the anode to the cathode
enables a current to flow. During recharging, the ions flow
the other way.
Carbon anodes have low capacity, which restricts the amount
of electrical energy they can store. So battery
technologists are searching for replacements with higher
capacities. Lithium cobalt nitride anodes are now under
development.
Lithium iron nitride has been investigated before as an
anode material, having a layered structure, and a capacity
about as large as the cobalt compound. But it has proved
hard to make. Nazar and her colleagues generate it cheaply
and quickly, by melting lithium nitride in iron vessels.
Ultimately, researchers would like to rid the cathode of
cobalt too. Some commercial lithium batteries use manganese
oxide instead, but it isn't stable enough for devices that
get hot, such as laptops. The search for a good alternative
continues.
References
Roswell, J. L.C., Pralong, V. & Nazar, L. F.Layered lithium
iron nitride: a promising anode material for Li-ion
batteries. Journal of the American Chemical Society, 123,
8598 - 8599, (2001). � Nature News Service / Macmillan
Magazines Ltd 2001
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. EV List Editor & RE newswires
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